1. Field of the Invention
This invention relates to tablet fabrication, and more particularly to the production of tablets through the use of a tableting press that compresses powders and granules.
2. Background Information
Tableting presses have long been utilized to manufacture tablets by compressing powders and granules. A typical tableting press uses a cylindrical die center made of steel, and steel punches, to compress the powder under relatively high pressures, typically up to about 10 to 15 tons per square inch. One result of the compression is the production of heat. This heat builds up on the face of punches and in the die and, over a relatively short period of time, tends to cause the powder to stick to the faces of the punches and sides of the die. Once the powder begins to stick to the die and/or to the punch faces, the integrity of the tablet is compromised, since as the faces of the punches pull apart to eject the tablet, the tablet sticks to the punch faces and breaks, or is broken or damaged by the friction with the cylindrical walls of the die. Moreover, any powder remaining on the punches and/or die walls tends to add to the volume of powder within the die, to disadvantageously alter the internal pressure of the tablets. Tablets formed under excessive pressure may not dissolve properly, while tablets formed under insufficient pressure tend to break prematurely.
In order to reduce the die and face heat, and reduce the sticking on the face of the punches and the sides of the dies, it has been common practice to add powdered lubricants to the powdered tablet composition. These lubricants generally encase the powdered granules to reduce the friction on the face of the punches and the sides of the die. Commonly used lubricants include magnesium stearate and other stearates, such as sodium stearate and calcium stearate. Stearates tend to be useful as lubricants because of their relatively high viscosity and insolubility in water, which helps prevent their breakdown when used to make compressed tablets.
While the use of stearates may be satisfactory in some applications, such as in the production of pharmaceuticals, their use tends to be undesirable in tablets that are dissolved in water prior to ingestion. Due to their hydrophobic nature, the stearates tend to float to the top of the water when a tablet made using stearates is dissolved in water, creating an undesirable metallic sheen or film on the surface of the water.
Thus, when manufacturing a water soluble tablet it is important to reduce or eliminate any insoluble material in the composition. One attempt to manufacture water soluble tablets involves replacing hydrophobic lubricants, such as stearates, with water soluble lubricants such as polyethylene glycol. While the use of such water soluble lubricants tends to reduce sticking on the sides of the die, these lubricants by themselves do not adequately prevent the tablet composition from sticking to the faces of the punches. This sticking problem is particularly acute when producing relatively large tablets, in which the tablet tends to be pulled apart when the punches separate prior to the tablet's ejection from the press. In particular, over multiple cycles, the composition adhered to the faces of the punches tends to accumulate to undesirable levels to the point at which uniform tablets may no longer be produced.
Thus, a need exists for an apparatus and method for fabricating water soluble tablets which overcomes the drawbacks of the prior art.